1. Field of the Invention
This invention relates in general to offset lithographic printing presses. In particular, the invention relates to a lithographic press having an improved form roller.
2. Description of Related Art
An offset lithographic printing press has a cylindrical plate cylinder, on which a negative of the text and illustrations to be printed has been etched by a type of photographic process. Dampening rollers apply water to the plate cylinder, and the water adheres to the plate cylinder, except where the text and illustrations are located.
A series of form rollers, or inking rollers, then apply a layer of ink to the plate roller. The ink adheres to the plate cylinder only where the text and illustrations are located.
The plate cylinder then presses the inked text and illustrations onto a rubber blanket cylinder. An impression cylinder then presses a sheet of paper against the blanket cylinder as the paper passes between the blanket cylinder and the impression cylinder. The inked text and illustrations on the blanket cylinder are transferred onto the paper.
The series of form rollers may include vibrators or oscillating rollers that are cooled to chill the ink and prevent moisture loss. The vibrators also oscillate back and forth to pass the ink evenly to the form rollers.
Sometimes, impurities or clumps of ink on the vibrators will cause the ink to be spread unevenly onto the form rollers. This causes small dots, or hickeys, to appear on the paper. An apparatus was needed to eliminate these unwanted hickeys.